Display device employing a reflective polarizer and a reflective diffuser between a light source and the display device

ABSTRACT

A display device includes a reflective polarizer beneath a liquid-crystal display panel, and a light diffusing plate and a lighting apparatus disposed beneath the reflective polarizer. In a reflective display mode, the display device presents a specular display resulting from a light ray reflected by the reflective polarizer and a diffusion display resulting from a diffused light. In a transmissive display mode, the display device presents a dark display and a diffusion display caused by the light diffusing plate.

TECHNICAL FIELD

The present invention relates to a display device and an electronicapparatus. More particularly, the present invention relates to atransflective display device having two modes of display.

DISCUSSION

Since a conventional display device employing TN (Twisted Nematic)liquid crystal or STN (Super-Twisted Nematic) liquid crystal adopts thestructure of a liquid-crystal display panel sandwiched between twopolarizers, the utilization of light is poor. A transflective displaydevice in particular suffers dark display during a reflective displaymode.

Referring to FIG. 14, a conventional transflective liquid-crystaldisplay device using a TN liquid-crystal display panel is now discussed.Referring to FIG. 14, there are shown an upper polarizer 130, a TNliquid-crystal display panel 140, a lower polarizer 170, a transflectiveplate 180, and a light source 210. Although FIG. 14 shows the componentsspaced apart from each other, they actually closely adhere to oneanother.

Discussed now is how white color is presented during a reflectivedisplay mode. A light ray 111 is linearly polarized in a directionparallel with the page bearing FIG. 14 by the upper polarizer 130, istwisted in a polarization direction 90° by the TN liquid-crystal displaypanel 140, becoming a light ray linearly polarized in a directionperpendicular to the page, and is then transmitted through the lowerpolarizer 170. Part of the light ray transmitted through the lowerpolarizer 170 is reflected by the transflective plate 180, and is againtransmitted through the lower polarizer 170. The light ray is thentwisted in a polarization direction 90° by the TN liquid-crystal displaypanel 140 and is thus linearly polarized in a direction parallel withthe page, and is then transmitted through the upper polarizer 130.

Because of its light absorbing feature, the lower polarizer 170 partlyabsorbs the light ray. This lowers the utilization of light, presentinga dark display during the reflective display mode.

In an effort to resolve this problem, we have proposed a transflectivedisplay device (see Japanese Patent Application No. 8-245346) in whichthe lower polarizer 170 is replaced with a reflective polarizer thatreflects a light ray component linearly polarized in a predetermineddirection while transmitting a light ray component linearly polarized ina direction perpendicular to the predetermined direction. Referring toFIG. 15, the transflective display device using this reflectivepolarizer is now discussed.

Referring to FIG. 15, there are shown a non-voltage applied area 605 ofthe TN liquid-crystal display panel and a voltage applied area 606 ofthe TN liquid-crystal display panel. There are also shown the upperpolarizer 130, an upper glass substrate 302, a lower glass substrate304, a reflective polarizer 160, a transmissive-absorbent layer 307, anda lighting apparatus 210.

The principle of the reflective display mode is now discussed. A lightray 601, which is linearly polarized in a direction parallel with thepage by the upper polarizer 130, is twisted in a polarization direction90° by the non-voltage applied area 605 of the TN liquid-crystal displaypanel, thereby becoming a light ray linearly polarized in a directionperpendicular to the page. The light ray is then reflected by thereflective polarizer 160, and is twisted in a polarization direction 90°by the non-voltage applied area 605 of the TN liquid-crystal displaypanel, thereby becoming a light ray linearly polarized in a directionparallel with the page. The light ray is then transmitted through theupper polarizer 130. When no voltage is applied to the TN liquid-crystalpanel, a white display is thus presented.

On the other hand, a light ray 603, which is linearly polarized in adirection parallel with the page by the upper polarizer 130, istransmitted through the voltage applied area 606 of the TNliquid-crystal display panel without any change in a polarizationdirection, and is transmitted through the reflective polarizer 160. Thelight ray is then absorbed by the transmissive-absorbent layer 307. Ablack display is thus presented when a voltage is applied to the TNliquid-crystal display panel.

During the transmissive display mode, a light ray 602 emitted from thelighting apparatus 210 passes through an aperture formed in thetransmissive-absorbent layer 307, and is linearly polarized in adirection parallel with the page by the reflective polarizer 160. Thelight ray is then twisted in a polarization direction 90° by thenon-voltage applied area 605 of the TN liquid-crystal display panel,thereby becoming a light ray linearly polarized in a directionperpendicular to the page, and is absorbed by the upper polarizer 130. Ablack display is thus presented when no voltage is applied to the TNliquid-crystal display panel.

A light ray 604 emitted from the lighting apparatus 210 passes throughan aperture formed in the transmissive-absorbent layer 307, and islinearly polarized in a direction parallel with the page by thereflective polarizer 160. The light ray is then transmitted through thevoltage applied area 606 of the TN liquid-crystal display panel with nochange in a polarization direction, and is transmitted through the upperpolarizer 130. A white display is thus presented when a voltage isapplied to the TN liquid-crystal display panel.

In the transflective display device using such a reflective polarizer, apositive-negative relationship is reversed between the display in thereflective display mode and the display in the transmissive displaymode. For this reason, a user has difficulty watching a display with thelighting apparatus 210 lit under an external light, and the displayunder such conditions is not adequate depending on the purpose of use.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a displaydevice that is free from a positive-negative reversal between thereflective display mode and the transmissive display mode. It is anotherobject of the present invention to provide an electronic apparatusemploying such a display device.

The above and other objects are provided by a display device includes areflective polarizer beneath a liquid-crystal display panel, and a lightdiffusing plate and a lighting apparatus disposed beneath the reflectivepolarizer. In a reflective display mode, the display device presents aspecular display resulting from a light ray reflected by the reflectivepolarizer and a diffusion display resulting from a diffused light. In atransmissive display mode, the display device presents a dark displayand a diffusion display caused by the light diffusing plate.

The present invention works on the above principle, and comprisespolarization axis varying means, first polarizing splitter meansdisposed on one side of the polarization axis varying means whichtransmits a light ray component linearly polarized in a first directionwhile reflecting or absorbing a light ray component linearly polarizedin a predetermined direction different from the first direction, secondpolarizing splitter means disposed on the other side of the polarizationaxis varying means which reflects a light ray component linearlypolarized in a second direction while transmitting a light ray componentlinearly polarized in a predetermined direction different from thesecond direction, lighting means disposed on the side of the secondpolarizing splitter means opposite to the polarization axis varyingmeans, and light diffusing means disposed between the second polarizingsplitter means and the lighting means which diffuses and reflects alight ray coming in from the second polarizing splitter means, whiletransmitting a light ray coming from the lighting means toward thesecond polarizing splitter means.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a reflective polarizer.

FIG. 2 illustrates the principle of a reflective display mode of thedisplay device of the present invention.

FIG. 3 illustrates the principle of a transmissive display mode of thedisplay device of the present invention.

FIG. 4 is an exploded, cross-sectional view showing a transflectivedisplay device of a first embodiment of the present invention.

FIG. 5 is an explanatory view showing a lighting apparatus used in thedisplay device of the first embodiment of the present invention.

FIG. 6 shows the surface configuration of a light guide used in thedisplay device of the first embodiment of the present invention.

FIG. 7 is an exploded, cross-sectional view showing the display deviceof a second embodiment of the present invention.

FIG. 8 illustrates the relationship between the polarization axis of thereflective polarizer 40 and the polarization axis of the reflectivepolarizer 60, both used in the display device of the second embodimentof the present invention.

FIG. 9 is an exploded, cross-sectional view showing the display deviceof a third embodiment of the present invention.

FIG. 10 is an exploded, cross-sectional view showing the display deviceof a fourth embodiment of the present invention.

FIG. 11 is an exploded, cross-sectional view showing the display deviceof a fifth embodiment of the present invention.

FIG. 12 illustrates the function of exit angle control means used in thethird and fourth embodiments of the present invention.

FIG. 13 is a perspective view showing an electronic apparatus of thepresent invention.

FIG. 14 is a cross-sectional view of a conventional transflectivedisplay device employing a structure in which a liquid crystal issandwiched between a pair of polarizers.

FIG. 15 is a cross-sectional view showing a conventional transflectivedisplay device employing a reflective polarizer.

DETAILED DESCRIPTION OF THE DRAWINGS

The principle of the present invention is now discussed referring toFIG. 1, FIG. 2 and FIG. 3. FIG. 1 is a perspective view of a reflectivepolarizer which is used as polarizing splitter means. FIG. 4 illustratesthe principle of display when an external light enters the displaydevice of the present invention, and FIG. 5 is an explanatory viewillustrating the principle of display when a light source lights.

Referring to FIG. 1, the reflective polarizer 160 has a structure inwhich two different types of layers, layer 1 (A layer) and layer 2 (Blayer), are alternately laminated. A refractive index (n_(AX)) of the Alayer 1 in the X direction is different from a refractive index (n_(AY))in the Y direction. The refractive index (n_(AY)) of the A layer 1 inthe Y direction is approximately equal to a refractive index (n_(BY)) ofthe B layer 2 in the Y direction.

The light ray component linearly polarized in the Y direction, out ofthe light ray incident at a right angle on a top surface 5 of thereflective polarizer 160, is transmitted through the reflectivepolarizer 160, and then exits from a bottom surface 6 as a light raylinearly polarized in the Y direction. Conversely, the light raycomponent linearly polarized in the Y direction, out of the light rayincident at a right angle on the bottom surface 6 of the reflectivepolarizer 160, is transmitted through the reflective polarizer 160, andexits from the top surface 5 as a light ray linearly polarized in the Ydirection. The Y direction is called a polarization axis.

Let t_(A) represent the thickness of the A layer 1 in the Z direction,t_(B) represent the thickness of the B layer 2 in the Z direction, and λrepresent the wavelength of an incident light.

    t.sub.A ·n.sub.AX +t.sub.B ·n.sub.BX =λ/2(1)

With the above equation established, the light ray component linearlypolarized in the X direction, out of the light ray, having a wavelengthλ, incident at a right angle on the top surface 5 of the reflectivepolarizer 160 is reflected by the reflective polarizer 160 as a lightray linearly polarized in the X direction. The linearly polarized lightray having a wavelength λ incident on the bottom surface 6 is reflectedby the reflective polarizer 160 as a light ray linearly polarized in theX direction. The X direction is called a reflection axis.

Equation (1) holds on the entire visible-light wave range by varying thethickness t_(A) of the A layer 1 in the Z direction and the thickness oft_(B) of the B layer 2 in the Z direction. This arrangement provides areflective polarizer which reflects a light ray linearly polarized inthe X direction as a light ray linearly polarized in the X directionwhile transmitting a light ray linearly polarized in the Y direction asa light ray linearly polarized in the Y direction, not only in a singlecolor but also in a white color light.

Stretched polyethylene naphtalate (PEN) is used for the A layer andcopolyester of naphtalen dicarboxylic acid and terephthalic or isothalicacid (coPEN) is used for the B layer in the reflective polarizer 160.The materials of the reflective polarizer of the present invention arenot limited to these materials, and any appropriate materials may beselected. Such a reflective polarizer is disclosed in detail in JapaneseUnexamined Patent Publication No. 9-506985(toku-hyo-hei 9-506985).

FIG. 2 illustrates the display device of the present invention under thepresence of an external light. The display device employs the TNliquid-crystal display panel 140 as polarization axis varying means. Theupper polarizer 130 is disposed on top of the TN liqui-dcrystal displaypanel 140. Arranged beneath the TN liquid-crystal display panel 140 arethe reflective polarizer 160, a light diffusing layer 150, a lightsource 190 and a reflective layer 200 in that order from below. Thepolarization axis of the polarizer 130 is perpendicular to thepolarization axis of the reflective polarizer 160.

In a voltage applied area 120 on the right-hand side, a natural ambientlight 121 is linearly polarized in a direction parallel with the page bythe polarizer 130, and is then transmitted through the TN liquid-crystaldisplay panel 140 with no change in polarization direction. The lightray is then reflected by the reflective polarizer 160, as a light raylinearly polarized in a direction parallel with the page, is transmittedthrough the TN liquid-crystal display panel 140 with no change inpolarization direction, and then exits from the polarizer 130. Since thereflective polarizer 160 reflects light in a specular reflectionfashion, the display device presents a bright display on screen onlywhen the light ray reflected from the reflective polarizer is seen at aright viewing angle to a screen. The display device presents a darkdisplay on screen when the light ray reflected from the reflectivepolarizer is viewed at viewing angles other than the right angle to thescreen.

In a non-voltage applied area 110 on the left-hand side, a naturalambient light 111 is linearly polarized in a direction parallel with thepage by the polarizer 130, and is twisted in a polarization direction90° by the TN liquid-crystal display panel 140, becoming a light raylinearly polarized in a direction perpendicular to the page. The lightray is then transmitted through the reflective polarizer 160, and ispartly transmitted through the light diffusing layer 150. The light raytransmitted through the light diffusing layer 150 is reflected by thereflective layer 200, is again transmitted through the light diffusinglayer 150, and exits toward the reflective polarizer. Part of the lightray transmitted through the reflective polarizer 160 is diffused throughand reflected by the light diffusing layer 150, and then exits towardthe reflective polarizer 160. The light ray linearly polarized in adirection perpendicular to the page, exiting to the reflective polarizerand transmitted again through the reflective polarizer 160, is twistedin a polarization direction 90° by the TN liquid-crystal display panel140, becoming a light ray linearly polarized in a direction parallelwith the page, and is then transmitted through the polarizer 130. Sincethe light ray transmitted through the polarizer 130 is a light raydiffused through the light diffusing layer 150, it is white in alldirections.

In the voltage applied area 120, the light reflected by the reflectivepolarizer 160 is an exiting light ray 122, while in the non-voltageapplied area 110, the light transmitted through the reflective polarizer160 is an exiting light 112, which looks white from all directions, as aresult of a diffusion action by the light diffusing layer 150. Under theexternal light, the display device presents a positive with a dark(black) display with a white background in almost all directions.However, a positive with a specular display with a white background isobtained in the reflection direction of the light ray reflected by thereflective polarizer.

Referring to FIG. 3, the liquid-crystal display device remains unchangedfrom the one shown in FIG. 2. In the voltage applied area 120 on theright-hand side, a light ray component aligned with the polarizationdirection of the reflective polarizer 160, out of a light ray 125 from alight source, is transmitted through the reflective polarizer 160 as alight ray linearly polarized in a direction perpendicular to the page.The light ray transmitted through the reflective polarizer 160 is thentransmitted through the TN liquid-crystal display panel 140 with nochange in polarization direction, and is absorbed by the polarizer 130.The resulting display thus appears black.

In the non-voltage applied area 110 on the left-hand side, a light raycomponent aligned with the polarization direction of the reflectivepolarizer 160, out of a light ray 115 from the light source, istransmitted through the reflective polarizer 160 as a light ray linearlypolarized in a direction perpendicular to the page. The light raytransmitted through the reflective polarizer 160 is then twisted in apolarization direction 90° by the TN liquid-crystal display panel,becoming a light ray linearly polarized in a direction parallel with thepage, and is then transmitted through the polarizer 130.

With the light source lit, the voltage applied area 120 presents a darkdisplay as a result of light absorption through the polarizer 130 whilethe non-voltage applied area 110 presents a light display as a result oflight transmission through the polarizer 130. A black positive with alight source color background is presented when the light source 190lights. In conclusion, a positive display is presented regardless ofwhether the display device is under the external light or with the lightsource lit.

The voltage applied area and the non-voltage applied area may bereversed in presentation by rotating the polarization axis of thepolarizer 130 by 90°. In this case, a negative display is presentedregardless of whether the display device is under the external light orwith the light source lit.

In the above discussion, the TN liquid-crystal display panel 140 isemployed. The basic principle of the present invention remains unchangedeven if another liquid-crystal display with its polarization axis variedby a voltage or the like, such as an STN liquid-crystal display panel orECB (Electrically Controlled Birefringence) liquid-crystal displaypanel, is alternatively employed.

The present invention works on the above principle, and comprisespolarization axis varying means, first polarizing splitter meansdisposed on one side of the polarization axis varying means whichtransmits a light ray component linearly polarized in a first directionwhile reflecting or absorbing a light ray component linearly polarizedin a predetermined direction different from the first direction, secondpolarizing splitter means disposed on the other side of the polarizationaxis varying means which reflects a light ray component linearlypolarized in a second direction while transmitting a light ray componentlinearly polarized in a predetermined direction different from thesecond direction, lighting means disposed on the side of the secondpolarizing splitter means opposite to the polarization axis varyingmeans, and light diffusing means disposed between the second polarizingsplitter means and the lighting means which diffuses and reflects alight ray coming in from the second polarizing splitter means, whiletransmitting a light ray coming from the lighting means toward thesecond polarizing splitter means.

Used for the polarization axis varying means is a liquid-crystal displaypanel, and preferably, a TN liquid-crystal display panel, an STNliquid-crystal display panel, or an ECB liquid-crystal display panel.The STN liquid-crystal display panels include the type employing anoptically anisotropic material for color correction. Preferably, thepolarizer is used for the first polarizing splitter means and thereflective polarizer described with reference to FIG. 3 is used for thesecond polarizing splitter means. The reflective polarizer describedwith reference to FIG. 3 may be used for the first polarizing splittermeans.

Preferably used for the lighting means is a lighting apparatus includinga light source as a light emitting body and a light guide plate foroutputting a light from the light source toward the light diffusingmeans. The light diffusing means needs to transmits the light coming infrom the lighting means toward the second polarizing splitter means.

With the lighting means lit, namely, during the transmissive displaymode, two display modes of dark and light displays are availabledepending on the state of the polarization axis of the polarization axisvarying means: in the dark display mode (hereinafter simply referred toas dark display), the light ray from the lighting means is nottransmitted through the first polarizing splitter means and in the lightdisplay mode (hereinafter referred to as diffusion display), the lightray from the light source is diffused through the light diffusing meansand is then transmitted through the first polarizing splitter means.

Under the external light, namely, during the reflective display mode,two display modes of specular display and diffusion display areavailable depending on the state of the polarization axis of thepolarization axis varying means: in the specular display mode(hereinafter referred to as specular display), the external light isreflected by the second polarizing and in the diffusion display mode(hereinafter referred to as diffusion display), the external light isdiffused and reflected by the light diffusing means. To present thespecular display, no diffusion layer is preferred in the optical path ofthe light reflected by the second polarizing splitter means. In thespecular display, a light display is presented only when the light rayreflected by the second polarizing splitter means is viewed from thedirection of reflection while a dark display is presented when the lightray reflected by the reflective polarizer is viewed from directionsother than the direction of reflection. The specular display generallylooks dark. On the other hand, the diffusion display looks light fromall directions. For this reason, a resulting contrast is free from anyparticular problem in presentation, though the two display modes makeuse of the exiting light from the polarizer.

In the above two display modes, the specular display in the reflectivedisplay mode corresponds to the dark display in the transmissive displaymode, and the diffusion display in the reflective display modecorresponds to the diffusion display in the transmissive display mode. Atransflective display device free from the reversal in thepositive-negative relationship is thus provided.

In the above arrangement, the light diffusing means may emit a colorlight ray. Specifically, a polymeric film containing colored micro-pearlmay be used for the light diffusing means.

The light diffusing means may emit a light ray. Specifically, afluorescent plate may be used for the light diffusing means, and thediffusion display appears in a fluorescence color.

Provided on the side of the lighting means opposite to the lightdiffusing means is light reflective means for reflecting a light raycoming in from the lighting means. The lighting means transmits a lightray coming in from the light diffusing means toward the light reflectivemeans, while transmitting a light ray coming in from the lightreflective means toward the light diffusing means.

In the diffusion display during the reflective display mode, theexternal light is partly reflected by and partly transmitted through thelight diffusing means. The light ray transmitted through the lightdiffusing means is transmitted through the lighting means, is reflectedby the reflective means, and is again transmitted through the lightdiffusing means. For this reason, the diffusion display in thereflective display mode is even lighter. In the diffusion display duringthe transmissive display mode, the light ray component linearlypolarized in the second predetermined direction, out of the light rayfrom the lighting apparatus, transmitted through the light diffusingmeans, is reflected by the second polarizing splitter means, and thereflected light ray is again reflected by the light reflective means. Asthe light ray is repeatedly reflected and diffused, the light ray ispartly varied in a polarization direction, and is then transmittedthrough the second polarizing splitter means. The light reflective meansreflects a light ray that is reflected toward the lighting apparatus bythe light diffusing means and a light ray component of the light rayemitted by the light source exiting toward the light reflective means.For this reason, the utilization of light is improved, presenting alighter diffusion display in the transmissive display mode.

The light reflective means may emit a light ray or a color light ray. Toemit a light ray, a fluorescent plate may be employed, and to emit acolor light ray, a hologram may be employed. With this arrangement, thediffusion displays in the transmissive display mode and reflectivedisplay mode are colored, providing an easy-to-sec feature to thedisplay device.

Light exit angle control means for outputting a light ray at an exitangle within a predetermined range may be further arranged between thelighting means and the light diffusing means or between the secondpolarizing splitter means and the light diffusing means.

A film including a plurality of layers having different refractiveindexes may be used for the light exit angle control means. Such a filmis, for example, Lumisty Film (trade name) manufactured by SUMITOMOCHEMICAL CO., LTD.

Referring to FIG. 12, the exit angle control means is now discussed.Designated 1000 is a film in which a Lumisty Film is disposed on top ofa light diffusing plate or a light reflector. A light ray 1001 isincident on the film 1000, and exits as a diffused light ray. Thestrongest light ray of the diffused light is now designated 1002. Theincident angle θ1 of the incident light ray 1001 is different from theexit angle of the exiting light ray 1002. When a light ray is incidentat an angle of θ1, the light ray reflected from the film exits at anexit angle of θ2. However, a light ray reflected by the secondpolarizing splitter means exits at an exit angle of θ1. With the deviceviewed at θ2, an increased contrast results.

Arranged between the lighting means and the light diffusing means isthird polarizing splitter means which reflects a light ray componentlinearly polarized in a third direction, while transmitting a light raycomponent linearly polarized in a predetermined direction different fromthe third direction. Like the second polarizing splitter means, thethird polarizing splitter means may be the reflective polarizerdescribed with reference to FIG. 3. By arranging the second polarizingsplitter means and the third polarizing splitter means with theirpolarization axes out of alignment, the light ray transmitted throughthe second polarizing splitter means is reflected by the thirdpolarizing splitter means in the diffusion display in the reflectivedisplay mode. The diffused light ray transmitted through the firstpolarizing splitter means is increased, resulting in a lighter diffuseddisplay. An excessively large angle set between the polarization axis ofthe second polarizing splitter means and the polarization axis of thethird polarizing splitter means makes it difficult for the light rayfrom the lighting apparatus to transmit through the second and thirdpolarizing splitter means. The diffusion display in the transmissivedisplay mode is thus darkened. If the angle between the two polarizationaxes is too small, most of the light ray transmitted through the secondpolarizing splitter means is also transmitted through the thirdpolarizing splitter means, reducing the effect of lighting the diffusiondisplay in the reflective display mode. The angle between thepolarization axis of the second polarizing splitter means and thepolarization axis of the third polarizing splitter means is preferablybetween 45° and 80°, and more preferably between 60° and 75°.

The reflective polarizer as the second polarizing splitter means or thethird polarizing splitter means is characterized by its laminatestructure in which layers having birefringence and layers having nobirefringence are alternately laminated. By adjusting the thickness ofeach layer in the lamination, a light ray in the visible-lightwavelength region having one polarization direction is reflected and alight ray in the visible-light wavelength region having anotherpolarization direction is transmitted therethrough, and the diffusiondisplay appears white.

The electronic apparatus of the present invention comprises a displaydevice with a liquid-crystal display panel as a display unit, whereinthe display device comprises a liquidcrystal display panel having aliquid crystal interposed between a pair of substrates, a polarizerdisposed on one side of the liquid-crystal display panel, a firstreflective polarizer disposed on the other side of the liquid-crystaldisplay panel, a lighting apparatus disposed on the side of the firstreflective polarizer opposite to polarization axis varying means, and alight diffusing plate which, arranged between the first reflectivepolarizer and the lighting means, diffuses and reflects a light raycoming in from the first reflective polarizer while transmitting a lightray coming in from the lighting apparatus toward the first reflectivepolarizer.

With the above arrangement, the electronic apparatus of the presentinvention is free from the positive/negative reversal.

The display device of the present invention finds applications in both apassive matrix addressing liquid-crystal display panel and an activematrix addressing liquid-crystal display panel in which the liquidcrystal is addressed by thin-film transistors or thin-film diodes formedon a substrate.

Referring again to the drawings, the preferred embodiments of thepresent invention are now discussed. FIG. 4 is an exploded,cross-sectional view showing the display device of a first embodiment ofthe present invention. The display device of the first embodiment is atransflective display device having two display modes, a reflectivedisplay mode and a transmissive display mode.

A display device 10 of the first embodiment employs an STNliquid-crystal display panel 20 for the polarization axis varying means.A retardation film 14 and a polarizer 12 are laminated on the STNliquid-crystal display panel 20 in that order therefrom. Arrangedbeneath the STN liquid-crystal display panel 20 are a reflectivepolarizer 40 as the first polarizing splitter means, a light diffusingplate 30 as the light diffusing means, a lighting apparatus 70 as thelighting means, and a reflector 90 as the light reflective means in thatorder from below. The reflective polarizer described with reference toFIG. 1 may be used for the reflective polarizer 40. The reflectivepolarizer 40 has a thickness within a range of 50 to 200 μm, and isglued onto a glass substrate 22 using acrylic adhesive therebetween. Thelight diffusing plate 30 preferably has a haze value within a range of 5to 85. A large haze value lowers the lightness on the screen whileresulting in a large viewing angle. The light diffusing plate 30 may bea resin in which micro-particles are dispersed, and the resin is appliedonto the surface of the reflective polarizer 40. A plastic film withaluminum or silver deposited thereon, or aluminum foil may be used forthe reflector 90. The thickness of the reflector 90 is preferably withina range of 10 μm to 200 μm.

In the STN liquid-crystal display panel 20, an STN liquid crystal 26fills a panel constructed of glass substrates 21 and 22 and sealingmembers 23. The thickness of each of the two glass substrates 21 and 22is 2 mm or thinner. A transparent electrode 24 is attached on theunderside of the glass substrate 21, and a transparent electrode 25 isattached on the top surface of the glass substrate 22. ITO (Indium TinOxide) or tin oxide may be used for the transparent electrodes 21 and22. The retardation film 14 is used as a color correction, opticallyanisotropic material to correct coloration generated by the STNliquid-crystal display panel 20. The lighting apparatus 70 employs anLED (Light Emitting Diode) 71, and projects light upward through a lightguide 72.

The lighting apparatus 70 is constructed as shown in FIG. 5. The lightguide 72 is made of polycarbonate or acrylic transparent plastic plateand has a width within a range of 0.3 mm to 2 mm, and has a number ofdimples or projections 73 on its surface. The dimples or projections,each having a size ranging from 10 μm to 200 μm, are spaced with a pitchof 20 μm to 400 μm. As shown, each projection or dimple may be asemispherical projection shown in FIG. 6(a), a conical dimple shown inFIG. 6(b), a semispherical dimple shown in FIG. 6(c), a circular columnprojection shown in FIG. 6(d), a circular column dimple shown in FIG.6(e), or any other shape. The density of dimples or projections may bechanged to provide a uniform surface luminance on the light guide 72.For its surface dimples or projections, the light guide 72 also servesas a light diffusing plate.

Preferably, the light guide has a small optical anisotropy. The presenceof optical anisotropy tends to cause discoloration or irregularcoloration in the display.

The operation of the transflective display device 10 of this embodimentis now discussed referring to FIG. 4. Under the external light, in avoltage applied area, the natural ambient light is linearly polarized ina predetermined direction by the polarizer 12, and is then twisted in apolarization direction a predetermined angle by the STN liquid-crystaldisplay panel 20, and is then reflected by the reflective polarizer 40rather than being absorbed. The light ray is then twisted in apolarization direction a predetermined angle by the STN liquid-crystaldisplay panel 20, and exits from the polarizer 12 as a linearlypolarized light ray. In the voltage applied area, the light ray is notabsorbed but reflected by the reflective polarizer 40, presenting aspecular display.

In a non-voltage applied area, the natural ambient light is linearlypolarized in a predetermined direction by the polarizer 12, and is thentransmitted through the STN liquid-crystal display panel 20 as alinearly polarized light ray, and is transmitted through the reflectivepolarizer 40 as a linearly polarized light ray. The linearly polarizedlight ray thus transmitted is diffused by the light diffusing plate 30.A light ray component transmitted through the light diffusing plate 30is reflected by the reflector 90, and is diffused by the light diffusingplate 30, and is transmitted through the STN liquid-crystal displaypanel 20 and polarizer 12, and exits as a linearly polarized light ray.Since the exiting light is a diffused light, it appears white.

The light ray reflected by the reflective polarizer 40 exits in alinearly polarized light ray featuring specularity in the voltageapplied area while the light ray transmitted through the reflectivepolarizer 40 is thus diffused through the light diffusing plate 30 andthen exits as a linearly polarized light ray presenting white color.With this arrangement, a specular display with a white background,namely, a dark display results.

With the light source lit, in a voltage applied area, the light rayemitted by the lighting apparatus 70 is transmitted through thereflective polarizer 40, and is then twisted in a polarization directiona predetermined angle by the STN liquid-crystal display panel 20becoming a light ray linearly polarized in a predetermined direction,and is absorbed by the polarizer 12. The voltage applied area thusappears black.

In a non-voltage applied area, the light ray from the light source istransmitted through the reflective polarizer 40, and is then twisted ina polarization direction a predetermined angle by the STN liquid-crystaldisplay panel 20 becoming a light ray linearly polarized in apredetermined direction, and is transmitted through the polarizer 12.

The light ray in the voltage applied area is absorbed by the polarizer12, becoming dark while the light ray in the non-voltage applied areaexits through the polarizer 12. A black display is presented with thecolor of the exiting light ray from the lighting apparatus as thebackground color.

The light diffusing plate 30 may be colored to change the backgroundcolor. When the polarizer 12 is replaced with a reflective polarizerhaving the same structure as that of the reflective polarizer 40, alight white display is presented under the external light because suchreflective polarizer is unable to absorb light unlike the polarizer 12.

When a green hologram was employed for the reflector 90, the diffusiondisplays in both the reflective display mode and the transmissivedisplay mode were green-colored at one viewing angle. When a prism sheetwas employed for the reflector 90, a black display with a lightbackground was presented at one viewing angle.

FIG. 7 is an exploded, cross-sectional view showing the display deviceof a second embodiment of the present invention. In the secondembodiment, a reflective polarizer 60 as the third polarizing splittermeans is arranged between the light diffusing plate 30 and the lightingapparatus 70. The rest of the construction of the second embodimentremains unchanged from that of the first embodiment, and the detaileddescription about it is not repeated here.

FIG. 8 illustrates the relationship between the polarization axis of thereflective polarizer 40 and the polarization axis of the reflectivepolarizer 60, wherein 41 designates the polarization axis of thereflective polarizer 40 and 61 designates the polarization axis of thereflective polarizer 60. In the second embodiment, the angle θ betweenthe polarization axis 41 and the polarization axis 61 is 68°.

The study of the display of the display device in the second embodimentrevealed that the diffusion display became lighter in the reflectivedisplay mode because the light ray transmitted through the reflectivepolarizer 40 was reflected by the reflective polarizer 60.

The further study of the display with the magnitude of θ changingrevealed the following tendency. With the angle θ decreasing, both thevoltage applied area and the non-voltage applied area were lighterbecause most of the light ray in alignment with the polarization axis61, which is transmitted through the reflective polarizer 60 with thelight source lit, is transmitted through the reflective polarizer 40.Under the external light, most of the light ray in alignment with thepolarization axis 41, which is transmitted through the reflectivepolarizer 40, is not reflected by the reflective polarizer 60. Thelightness of the non-voltage applied area is not so much heightened.With the angle θ between the polarization axis 41 and the polarizationaxis 61 decreasing, the transmissive display mode offers a lightdisplay, while the non-voltage applied area in the reflective displaymode is darkened. Conversely, with the angle θ between the polarizationaxis 41 and the polarization axis 61 increasing, the transmissivedisplay mode presents a dark display, while the non-voltage applied areain the reflective display mode becomes light. The angle θ has its ownappropriate range. According to test results, the angle θ is preferablywithin a range of 45° to 80°, and is more preferably within a range of60° to 75°.

FIG. 9 is an exploded, cross-sectional view showing the liquid-crystaldisplay device of a third embodiment of the present invention. In thethird embodiment, a Lumisty Film, manufactured by SUMITOMO CHEMICAL CO.,LTD, as the exit angle control means, was arranged between the lightdiffusing plate 30 and the reflective polarizer 40. Since the rest ofthe construction of the third embodiment remains unchanged from that ofthe second embodiment, the detailed discussion about it is not repeated.

The light diffusing plate 30 contains micro-pearl dispersed therein andis a transflector serving also as reflective means. Lumisty 80,manufactured by SUMITOMO CHEMICAL CO., LTD., in combination with thelight diffusing plate 30, has the effect of making the light exit angledifferent from the light incident angle as shown in FIG. 12. This isbecause Lumisty Film has the following structure and characteristics.Lumisty Film contains layers having different refractive indexes, eachhaving a thickness of 3 μm. This laminate structure causes lightdiffraction, diffusing light. By adjusting the laminate structure, thedirection of the diffuse light is controlled. When an incident angle is70°, an exit angle becomes 90°. Even when the screen of the device isviewed at a right angle and shadowed by a user, the screen is notdarkened and remains light. With this arrangement, the device screen iseasy to view with an increased contrast. A removal of the retardationfilm 14 resulted in a blue display with a bright yellow background.

FIG. 10 is an exploded, cross-sectional view of the liquid-crystaldisplay device of a fourth embodiment of the present invention. In thefourth embodiment, Lumisty Film, manufactured by SUMITOMO CHEMICAL, CO.,LTD, as the exit angle control means, was arranged between the lightingapparatus 70 and the reflector 90. The rest of the construction of thefourth embodiment remains unchanged from that of the first embodiment,and the detailed description about it is not repeated here.

With this arrangement, like the third embodiment, the screen is notdarkened and remains light, and is easy to view with an increasedcontrast, even when the screen of the device is viewed at a right angleand shadowed by a user. When the light source is lit, the device screenis lighter than the one in the third embodiment.

FIG. 11 is an exploded, cross-sectional view of the display device of afifth embodiment of the present invention. In the fifth embodiment, afluorescent body 81 was arranged on the back surface of the lightingapparatus 70. The rest of the construction of the fifth embodimentremains unchanged from that of the first embodiment, and the detaileddescription about it is not repeated here.

With this arrangement, the fluorescent plate 81 is exposed to light bothunder the external light and with the light source lit, causing thescreen to be light. The same effect results even if the fluorescentplate 81 is arranged between the lighting apparatus 70 and thereflective polarizer 40.

FIG. 13 shows the sixth embodiment of electronic apparatuses thatincorporate the display device of the first embodiment. FIG. 13(a) showsa portable telephone, FIG. 13(b) shows a watch, FIG. 13(c) shows apersonal computer. The electronic apparatuses of the sixth embodimentpresented a bright display screen under daylight, shade, indoor andnighttime conditions. Any of the display devices of the first embodimentand third to fifth embodiments may be incorporated in the electronicapparatus of the sixth embodiment.

The display device of the present invention finds applications in adiversity of apparatuses, besides the above apparatuses, including homeelectronics, PDAs (Personal Digital Assistants), electronic pocketbooks,and calculators.

Under the external light, the display device of the present inventionpresents two display modes, namely the specular display mode resultingfrom the light ray reflected by the second polarizing splitter means andthe diffusion display mode resulting from the diffused light ray fromthe light diffusing means, depending on the state of the polarizationaxis of the polarization axis varying means. In the specular displaymode, the display screen is dark except for a viewing angle equal to theincident angle. In the diffusion display mode, the display screen islight in all directions. With the light source lit, the display deviceof the present invention presents the two display modes, namely, thedark display mode in which no light is transmitted through the firstpolarizing splitter means and the diffusion display mode resulting fromthe diffused light transmitted through the first polarizing splittermeans, depending on the state of the polarization axis of thepolarization axis varying means. The transflective display device thuspresents a light positive display during the reflective display mode andalso presents a positive display during the transmissive display mode.

Preferably, the reflective means is disposed on the side of the lightdiffusing means opposite to the second polarizing splitter means. Withthis arrangement, the display screen is light both in the reflectivedisplay mode and the transmissive display mode.

What is claimed is:
 1. A display device comprising:polarization axisvarying means; first polarizing splitter means disposed on one side ofsaid polarization axis varying means which transmits a light raycomponent linearly polarized in a first direction while reflecting orabsorbing a light ray component linearly polarized in a predetermineddirection different from said first direction; second polarizingsplitter means disposed on another side of said polarization axisvarying means which reflects a light ray component linearly polarized ina second direction while transmitting a light ray component linearlypolarized in a predetermined direction different from said seconddirection; lighting means disposed on a side of said second polarizingsplitter means opposite to said polarization axis varying means; andlight diffusing means disposed between said second polarizing splittermeans and said lighting means which diffuses and reflects a light raycoming in from said second polarizing splitter means, while transmittinga light ray coming from said lighting means toward said secondpolarizing splitter means.
 2. A display device according to claim 1,wherein said light diffusing means transmits a color light ray.
 3. Adisplay device according to claim 1, wherein said light diffusing meanstransmits a light ray.
 4. A display device according to claim 1, furthercomprising light reflective means disposed on a side of said lightingmeans opposite to said light diffusing means for reflecting a light raycoming in from said lighting means, wherein said lighting meanstransmits a light ray coming in from said light diffusing means towardsaid light reflective means, while transmitting a light ray coming infrom said light reflective means toward said light diffusing means.
 5. Adisplay device according to claim 4, wherein said light reflective meansreflects a light ray.
 6. A display device according to claim 4, whereinsaid light reflective means reflects a color light ray.
 7. A displaydevice according to claim 1, further comprising light exit angle controlmeans disposed between said second polarizing splitter means and saidlight diffusing means for outputting a light ray at an exit angle withina predetermined range when receiving a light ray.
 8. A display deviceaccording to claim 1, further comprising light exit angle control meansdisposed between said lighting means and said light diffusing means foroutputting a light ray at an exit angle within a predetermined rangewhen receiving a light ray.
 9. A display device according to claim 1,further comprising third polarizing splitter means disposed between saidlighting means and said light diffusing means which reflects a light raycomponent linearly polarized in a third direction, while transmitting alight ray component linearly polarized in a predetermined directiondifferent from said third direction.
 10. A display device according toclaim 9, wherein said second polarizing splitter means and said thirdpolarizing splitter means are disposed such that said second directionand said third direction are different from each other.
 11. A displaydevice comprising:a liquid-crystal display panel having a liquid crystalinterposed between a pair of substrates; a polarizer disposed on oneside of said liquid-crystal display panel; a first reflective polarizerdisposed on another side of said liquid-crystal display panel; alighting apparatus disposed on a side of said first reflective polarizeropposite to said liquid-crystal display means; and a light diffusingplate disposed between said first reflective polarizer and said lightingapparatus which diffuses and reflects a light ray coming in from saidfirst reflective polarizer, while transmitting a light ray coming infrom said lighting apparatus toward said first reflective polarizer. 12.A display device according to claim 11, wherein said diffusing plate isa fluorescent plate.
 13. A display device according to claim 11, furthercomprising a reflector on a side of said light diffusing plate oppositeto said lighting apparatus, wherein said lighting apparatus comprises alight source and a substantially transparent light guide.
 14. A displaydevice according to claim 13, wherein said reflector is a hologram. 15.A display device according to claim 13, wherein said reflector is afluorescent plate.
 16. A display device according to claim 11, furthercomprising a film including a plurality of layers having differentrefractive indexes laminated together and disposed between said firstreflective polarizer and said light diffusing plate.
 17. A displaydevice according to claim 11, further comprising a film including aplurality of layers having different refractive indexes laminatedtogether and disposed between said lighting apparatus and said lightdiffusing plate.
 18. A display device according to claim 11, furthercomprising a second reflective polarizer disposed between said lightdiffusing plate and said lighting apparatus.
 19. A display deviceaccording to claim 18, wherein said first reflective polarizer and saidsecond reflective polarizer are arranged such that polarization axis ofeach polarizer is out of alignment with the other.
 20. A display deviceaccording to claim 11, wherein said first reflective polarizer is alaminate of a plurality of layers having birefringence and a pluralityof layers having no birefringence in which one layer havingbirefringence and one layer having no birefringence are alternatelylaminated.
 21. An electronic apparatus having a display device with aliquid-crystal display panel as a display unit, said display devicecomprising:a liquid-crystal display panel having a liquid crystalinterposed between a pair of substrates; a polarizer disposed on oneside of said liquid-crystal display panel; a first reflective polarizerdisposed on another side of said liquid-crystal display panel; alighting apparatus disposed on a side of said first reflective polarizeropposite to said liquid-crystal display panel; and a light diffusingplate disposed between said first reflective polarizer and said lightingapparatus which diffuses and reflects a light ray coming in from saidfirst reflective polarizer while transmitting a light ray coming in fromsaid lighting apparatus toward said first reflective polarizer.